This invention relates to apparatus for the separation of liquids and particulate solids.
Many kinds of pressure filter have been described. One kind of pressure filter which has been found to be especially useful for separating liquids and very fine particulate solids is a tube pressure filter which comprises a pair of coaxial, generally tubular inner and outer assemblies arranged one within the other and adapted to be supported in a generally upright position, an impermeable elastic sleeve disposed within and secured to the outer tubular assembly, a filter element disposed around and supported by the inner tubular assembly, outlet means for the discharge from the interior of the inner tubular assembly of filtrate (i.e. liquid) which has passed through the filter element and through apertures in the inner tubular assembly, and means for displacing the tubular assemblies axially relative to one another between first and second positions, the arrangement being such that in the first position of said tubular assemblies they co-operate with each other to define a closed chamber of annular cross-section which is divided into coaxial and non-intercommunicating inner and outer compartments by said impermeable elastic sleeve, the inner compartment having an inlet for feed material comprising a mixture of a liquid and a particulate solid to be separated and the outer compartment having an inlet for a hydraulic fluid under pressure, and in the second position of said tubular assemblies said chamber of annular cross-section is open to enable the particulate solid to be discharged from the inner compartment. Hereinafter such a tube pressure filter will be referred to as a "tube pressure filter of the kind set forth". Tube pressure filters of the kind set forth have been described, for example, in British patent specification Nos. 907,485 and 1,240,465.
In a tube pressure filter of the kind set forth the inner tubular assembly and the filter element disposed around and supported thereby are constructed and arranged so that, in use, when the tubular assemblies are in their first position, liquid from the mixture of the liquid and particulate solid can be forced through the filter element and through apertures in the inner tubular assembly while the particulate solid from said mixture is retained on the filter element, the liquid being forced through the filter element by the introduction of a hydraulic fluid under pressure into the outer compartment (the hydraulic fluid urging the impermeable elastic sleeve towards the filter element so as to compress the mixture in the inner compartment and express liquid therefrom); and so that, in use, when the tubular assemblies are in their second position and the chamber of annular cross-section is open, said particulate solid can be discharge from the inner compartment. The filter element usually comprises a sleeve of filter cloth material which is advantageously supported on a wire mesh screen held around the inner tubular assembly of the tube pressure filter. Such a filter element is described in more detail in British patent specification No. 1,317,887.
Conveniently, the inner tubular assembly of a tube pressure filter of the kind set forth comprises a cylindrical central section, around which central section there is disposed the filter element, and upper and lower end sections secured one to each end of said cylindrical central section, each of which end sections includes a portion (which cooperates with an adjacent portion of the outer tubular assembly to close the chamber of annular cross-section when said tubular assemblies are in their first position) of greater diameter than said cylindrical central section and a fairing mounted on or adjacent to said portion so as to extend around an end of the central section. Each fairing constitutes means whereby a gradual reduction of diameter occurs from said portion of greater diameter than the central section to said central section, i.e. the outwardly facing surface of the fairing slopes inwardly from the rim of said portion of greater diameter than the central section to said central section. The outwardly facing surface of the fairing can be linear or curved, in the latter case with either a concave or convex profile.